1. Field
Example embodiments relate to optical discs. Also, example embodiments relate to focus layer jump control circuits of optical discs and methods of controlling focus layers jumps used by the focus layer jump control circuits.
2. Description of Related Art
To obtain data written in a pit of an optical disc, a laser beam is projected to the optical disc and light reflected from the projected laser beam is picked up. The picked up, reflected light is converted into a radio frequency (RF) signal using an optical element such as a photo diode. A tracking error (TE) signal, a focus error (FE) signal, and an information signal are extracted from the RF signal. The TE signal controls an actuator driver to follow a track of the optical disc. The FE signal controls a focus actuator driver that controls a focus actuator in an exact position so that a focus of the projected laser beam on the optical disc can be adjusted.
The optical disc arranges pits in a layer located at a specific depth from the surface thereof. A dual-layer optical disc arranges pits in at least two layers, each having a different depth from the surface thereof, and writes data in one of the at least two layers, thereby increasing an amount of writing in the optical disc. Unlike the optical disc that writes data in one layer, the dual-layer optical disc requires a layer-jump operation. That is, to reproduce data written in the two layers, the dual-layer optical disc must layer jump from one layer to the other layer.
FIG. 1 is a waveform for generating a kick/brake signal in performing a related art layer jump using a FE signal. Referring to FIG. 1, if a layer jump command is applied, a S-shaped curve of the FE signal is used to generate a kick signal and a brake signal for driving a focus actuator.
The kick signal and the brake signal are indicated as a signal in the bottom of FIG. 1. The kick signal with a voltage level VK provides physical force to the focus actuator to move the focus actuator. The brake signal with the voltage level VB suppresses the physical force applied to the focus actuator.
When a layer of an optical disc is tracked, if a layer jump command (L/J) is applied to enable the kick signal, a waveform of the FE signal changes according to the motion of the focus actuator in response to the kick signal.
The change of the FE signal is smaller from the center line when the FE signal performs tracking. If the layer jump command (L/J) is applied to enable the kick signal, the width of the change of the FE signal increases according to the motion of the focus actuator in response to the kick signal.
If a S-shaped waveform of the FE signal in the bottom of the center line is formed in layer 0, and a S-shaped waveform of the FE signal in the upper of the center line is formed in layer 1, the layer jump command (L/J) indicates a jump from the layer 0 to the layer 1.
A time period where a magnitude of the FE signal is greater than or equal to a magnitude of a first reference voltage V1 until the magnitude of the FE signal is smaller than a magnitude of a second reference voltage V2 is a first time period T1. When the magnitude of the FE signal is smaller than the magnitude of the second reference voltage V2, the kick signal is disabled. Thus, the kick signal is enabled during a second time period T2. The focus actuator moves using a force supplied according to the kick signal after the kick signal is disabled. A time period where the focus actuator moves is a time from when the kick signal is disabled until the magnitude of the FE signal is greater than a magnitude of a fourth reference voltage V4. The time period is a third time period T3.
The brake signal is enabled from an end of the third time period T3 until a fourth time period T4 having a length equal to one half of the first time period T1 (i.e., T4=T1/2). When the magnitude of the FE signal is smaller than a magnitude of a fifth reference voltage V5, after the fourth time period T4, the layer jump is completed and a light pickup is changed to a pull-in mode.
The third time period T3 must be narrowed. A reference value T_ref used to determine a voltage level VB of the brake signal is a time period twice as long as the third time period T3 (i.e., T_ref=2*T3).
The voltage level VB of the brake signal is determined based on a comparison value COMPARE obtained by equation (1).COMPARE=T3−T_ref  (1)
Wherein the comparison value COMPARE denotes a difference in time between the third time period T3 and the reference value T_ref.
A jump from the layer 1 to the layer 0 will now be described.
If the comparison value COMPARE is smaller than 0, the voltage level VB of the brake signal is set to a previously set maximum value. If a value obtained (by subtracting a value obtained by multiplying data stored in an address 0 with data stored in an address 20 from the comparison value COMPARE) is greater than 0, the voltage level VB of the brake signal is set to the previously set reference value. In addition, a value stored in data of an address COMPARE+0×E0 is set to the voltage level VB of the brake signal. 0×E0 denotes a value obtained by multiplying the data stored in the address 0 with data stored in an address E0.
When a jump is performed from the layer 0 to the layer 1, if the comparison value COMPARE is smaller than 0, the voltage level VB of the brake signal is set to a previously set minimum value. If a value obtained (by subtracting a value obtained by multiplying the data stored in the address 0 with the data stored in the address 20 from the comparison value COMPARE) is greater than 0, the voltage level VB of the brake signal is set to the previously set reference value. In addition, a value stored in data of the address COMPARE+0×E0 is set to the voltage level VB of the brake signal.
The kick signal and the brake signal used for the layer jump of a related art digital versatile disc (DVD) dual disc have pulse waveforms, and thus have the following disadvantages.
1. Since a focus kick signal has a pulse waveform, it is difficult to control the accelerating force of the actuator.
2. Since the brake signal has the pulse waveform, if brakes controlled by the brake signal are too strong, the focus actuator can be returned to an original layer. If brakes controlling the brake signal are too weak, the focus actuator can be returned to a new layer but a focus pull-in can be impossible.
3. If a layer is off track after the layer jump, no focus-range signal is input and no control is performed. Therefore, since the focus pull-in must be performed again, a screen temporarily stops reproduction of the dual-layer optical disc.